It is known that patterned or selective metal plating can be achieved by chemical or electroless (two terms are interchangeably used in the art) metal deposition in which masking is employed to delineate the patterns. While masking plating techniques provide finely delineated patterns of metal which are now extensively needed in the manufacture of, for example, electronic circuits on dielectric substrates, these processes are inefficient and costly. Besides they may impose serious restriction on the size of the pattern which can be batch-deposited.
In U.S. Pat. No. 4,239,789 to BLUM et al there is described a maskless chemical plating method in which a surface of a workpiece is contacted with an electroless plating solution and an energy beam such as laser beam is directed onto the workpiece to locally heat the surface to promote enhanced plating. According to the teachings of that patent, the plating substrate is a nickel film vapor-deposited on a glass work-piece. The argon laser beam is passed through a nickel electroless plating solution and illuminates selected regions of the surface of the nickel film in contact therewith. The beam alternatively is passed through both the solution and the glass base and illuminates the nickel-glass interface beneath such regions of the surface of the nickel film in contact with the nickel electroless plating solution. While it is taught that there occurs localized enhancement of electroless nickel plating at those regions, the data offered indicate that the process disclosed is rather a low plating rate and slow-yield process. Even more of significance, there is no indication that a dielectric substrate such as glass can be directly pattern-plated without masking. Thus, the teaching of the BLUM et al patent which requires on a dielectric workpiece a nickel film for electroless nickel pattern plating is not properly applicable where as contemplated by applicant here a given metal (such as nickel) is to be selectively plated on a dielectric substrate to provide a delineated pattern of the metal thereon.